Power consumption for wireless communications will comprise a significant portion of platform power for small form-factor devices such as mobile internet devices/handhelds, etc. Energy-efficient protocols, therefore, are important to prolong the limited battery life of such devices.
While several MAC layer protocols exist for maximizing the sleep and idle modes to save battery power, optimizing the energy efficiency of transmissions in the active (transmitting or receiving) mode is also important to prolong the talk-time available to mobile devices. Thus far, this optimization problem has been studied largely in the context of short-range ad-hoc or sensor networks. There has been limited work on energy-efficient link adaptation and resource allocation for long-range, cellular type networks.
Additionally, the application of minimal energy link adaptation and resource allocation schemes to orthogonal frequency division multiple access (OFDMA) based wireless networks, such as WiMAX, has not been addressed in the literature. (WiMAX is short for worldwide interoperability for microwave access—the group promoting the IEEE 802.16 wireless broadband standard.)
In the prior art, a large body of work focuses on short-range communication systems, like sensor networks, where circuit energy dominates the energy consumption during the working lifetime of a node. Here, it is desirable to always use the highest supported modulation rate to complete transmissions as soon as possible. Additionally, for minimal circuit energy consumption, traffic transmissions may also be managed to maximize the sleep period. In long-range networks like cellular networks, the transmission energy dominates the total energy consumption. In order to minimize the transmission energy, the lowest modulation is preferred for such systems, while accommodating the delay constraint. Based on a similar idea, one prior art proposal involves a lazy packet scheduling scheme. This scheme minimizes the overall transmit energy, by extending the transmission time of each packet to be as long as permitted by the buffer backlog status.
In prior art energy-efficient link adaptation, considering the trade-offs between transmit energy and circuit energy consumption is described, but the treatment does not address multi-channel modulations such as OFDMA. Besides optimizing link transmissions, recent research also considers network optimization for energy efficiency. For example, a distributed power control approach is proposed for the uplink transmission of a code-division multiple access (CDMA) system. Additionally, joint user-centric and network-centric optimizations are considered to maximize the number of bits transmitted per joule.
Thus, there is a continuing need for energy-efficient link adaptation for wireless OFDMA systems.